Drivetrain device of a vehicle with a gear unit

ABSTRACT

A device ( 2 ) for a vehicle drivetrain ( 1 ) with a transmission unit ( 3 ) for changing various transmission ratios and with a hydraulic device ( 4 ). The device ( 2 ) can provide a drive torque in the area of the drive output ( 5 ) of the vehicle drivetrain ( 1 ) and in whose area a drive output torque of the vehicle drivetrain ( 1 ) can be at least partially supported. A reversing gear system ( 6 ) is connected, upstream of the transmission unit ( 3 ), for reversing the rotation direction and the hydraulic device ( 4 ) can be brought into active connection with the transmission unit ( 3 ) by way of the reversing gear system ( 6 ).

This application claims priority from German patent application serialno. 10 2009 001 602.3 filed Mar. 17, 2009.

FIELD OF THE INVENTION

The invention concerns a device for a vehicle drivetrain.

BACKGROUND OF THE INVENTION

A device for a vehicle drivetrain with a power branching transmissionand a reversing or turnover gear system is known from DE 10 2007 018 999A1. A drive input of the power branching transmission drives a planetarygear unit via the reversing gearing, in the area of which the power isdivided between a hydraulic power branch and a mechanical power branch.The hydraulic power branch consists of a pump and two motors. Inaddition, a hydraulic supply pump is connected to the drive of the powerbranching transmission, which supplies pressure fluid to the closedcircuit of the hydraulic pump and hydraulic motors in the sense of afeed pump.

Disadvantageously, however, neither in traction operation nor in thrustoperation can a drive torque be produced at the drive output of avehicle drivetrain or an applied drive output torque be supported bymeans of the additional hydraulic device or the hydraulic supply pump.Moreover, by means of the hydraulic device no recuperative operation canbe carried out, during which a thrust torque in the drivetrain can beused to recover energy and by virtue of which a vehicle can be operatedmore efficiently.

A hydrostatic drive with which braking energy can be recovered isdescribed in DE 10 2006 060 014 A1. The hydrostatic drive is formed witha hydro-pump and a hydro-motor connected to one another by a first and asecond working line. Furthermore, the hydrostatic drive is made with afirst reservoir and a second reservoir, the first reservoir beingdesigned for the storage of pressure energy and being connected to thefirst working line by a first seat valve and to the second working lineby a second seat valve. The second reservoir can be connected to thefirst working line by a third seat valve and to a second working line bya fourth seat valve.

Disadvantageously, this hydrostatic drive is characterized by a complexstructure and high production costs, for which reasons the drive is onlyof restricted suitability for use in a hybrid vehicle drivetrain.

SUMMARY OF THE INVENTION

Thus, the purpose of the present invention is to provide a device for avehicle drivetrain with a transmission unit for changing varioustransmission ratios and with a hydraulic device, which is characterizedby a simple and inexpensive structure and by means of which, at thedrive output of a vehicle drivetrain, both a drive torque can beprovided and an output torque can be supported by means of the hydraulicdevice.

The device according to the invention for a vehicle drivetrain is madewith a transmission unit for changing various transmission ratios andwith a hydraulic device. By means of the hydraulic device a drive torquecan be produced at the drive output of the vehicle drivetrain. Inaddition, in the area of the hydraulic device a drive output torque ofthe vehicle drivetrain can be at least partially supported. On thetransmission input side a reversing gear system is connected upstreamfrom the transmission unit in order to enable the rotation direction tobe reversed. The hydraulic device can be brought into active connectionwith the transmission unit via the reversing gear system.

In a simple manner, the preferably direct connection of the hydraulicdevice to the drive input of the vehicle drivetrain and to thetransmission unit via the reversing gearing makes it possible to use thefunctionality of the hydraulic device over the full operating range,i.e. over the entire speed range of the vehicle and also in both drivingdirections. In addition, the torque to be provided by the hydraulicdevice in each case is low by virtue of the connection of the hydraulicdevice on the transmission input side, since it is adapted by thetransmission ratio set in the area of the transmission unit to theoperating condition of the vehicle drivetrain at the time and isavailable, correspondingly transformed, at the drive output of thevehicle drivetrain.

The connection of the hydraulic device to the transmission unit via thereversing gear system also has the advantage that the device can be madewithout an additional axle spindle when the hydraulic device can bemounted in the area of the available axle separation to the drive flangeof the transmission unit.

If this is not possible because of the external dimensions of thehydraulic device, the hydraulic device can also be coupled by thereversing gearing to the transmission unit via an additional axlespindle, by virtue of which a larger axle distance to the drive flangeof the transmission unit can be made available. Then, the device can bemade with hydraulic devices that are more high-powered. Furthermore, anadditional axle spindle offers the possibility of providing atransmission ratio between the hydraulic device and the transmissionunit because of the larger structural space available, within a largetransmission ratio range adapted with great flexibility to theapplication concerned.

If the feasible axle separations do not suffice for the directincorporation of the hydraulic device with or without an additional axlespindle, it is also possible to mount the hydraulic device the requireddistance away from the transmission unit in the vehicle and connect itto the transmission unit by means of a universal shaft, and in such adesign of the device according to the invention only one drive flange isneeded in the area of the transmission unit.

In an advantageous further development of the device according to theinvention, a plurality of range clutches are provided in the area of theoutput of the transmission unit for producing various transmission ratioranges, within each of which the transmission ratio of the transmissionunit can be varied continuously. Thus, a vehicle made with the devicecan be operated over a large speed range, optimally adapted to theoperating condition of the vehicle in each case.

In a simply designed further development of the device according to theinvention that can be actuated with little effort, the hydraulic devicecan be brought into active connection, via a gearwheel, with a gearwheelof the reversing gear system.

To obtain start-stop operation, in a further advantageous embodiment ofthe device according to the invention the hydraulic device is connectedto an auxiliary drive output shaft. In this embodiment a drive machinecoupled to the auxiliary drive output shaft is entrained duringrecuperative operation of the hydraulic unit without a distinctseparating clutch, whereby the efficiency is impaired during therecuperative operation.

An embodiment of the device according to the invention that is favorablein terms of structural space comprises a hydraulic machine of thehydraulic device, which can be operated in both rotation directions.

To be able in a simply designed manner to provide at the drive output ofthe vehicle drivetrain a drive torque by means of the hydraulic device,or at least partially to support in its area an output torque of thevehicle drivetrain and preferably to be able to recover braking energyin the area of the hydraulic device, in an advantageous furtherdevelopment of the device according to the invention the hydraulicmachine is in active connection on its pressure side with a pressuremedium container unit and on its suction side with a hydraulic fluidreservoir.

A further development of the device characterized by a structure ofsimple design comprises, between the pressure side of the hydraulicmachine and the pressure medium container unit, a one-way valve that canbe actuated, which blocks the connection between the hydraulic machineand the pressure medium container unit, if there is a positive pressuregradient between the pressure medium container unit and the pressureside of the hydraulic machine.

In a simply actuated embodiment of the device according to theinvention, the one-way valve device can be actuated by a 3/2-way valve.

To avoid unacceptably high loads in the area of the hydraulic device, ina further development of the device according to the invention thehydraulic device comprises a pressure-limiting valve device for limitingthe maximum operating pressure.

An embodiment of the device according to the invention which is alsosimple to operate, is formed with a pressure sensor for monitoring astorage pressure of the pressure medium container unit.

To be able to obtain pure hybrid driving operation as free from lossesas possible by means of the hydraulic device, between the area where thehydraulic device and the reversing gear system are connected and an areaof the vehicle drivetrain in which a drive machine of the vehicledrivetrain can be coupled to the reversing gear system, a shift elementcan be provided in order to enable the active connection between thedrive machine and the reversing gearing, and the hydraulic device thatcan be coupled thereto, to be optionally formed.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and advantageous further developments of the inventionemerge from the claims and from the example embodiment whose principleis described with reference to the drawing, which shows:

FIG. 1: A very schematic representation of a vehicle drivetrain madewith the device according to the invention; and

FIG. 2: A detailed representation of the vehicle drivetrain according toFIG. 1

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a vehicle drivetrain 1 of a vehicle made as a workingmachine such as a wheel loader or an agricultural machine. The vehicledrivetrain 1 is made with a device 2 which in the present casecomprises, inter alia, a transmission unit 3 for changing varioustransmission ratios and a hydraulic device 4. By means of the hydraulicdevice 4, during traction operation a drive torque can be produced inthe area of a drive output 5 of the vehicle drivetrain 1. Furthermore,during thrust operation of the vehicle drivetrain 1, in the area of thehydraulic device 4 a drive output torque of the vehicle drivetrain 1 canbe supported, at least in part.

Upstream from the transmission unit 3 on its transmission input side isconnected a reversing gear system 6 for enabling a reversal of therotation direction, the hydraulic device 4 being arranged in the powerflow of the vehicle drivetrain 1 between a drive machine 7 of thevehicle drivetrain 1 and the reversing gear system 6. This means that inthe area of the reversing gearing 6, the operating mode can be switchedbetween forward and reverse driving.

In the connection area between the drive machine 7 of the vehicledrivetrain 1, in this case in the form of an internal combustion engine,and the reversing gear system 6, a so-termed auxiliary drive output 8branches off, by means of which various appliances of the vehicle madewith the vehicle drivetrain 1 can be driven, depending on the state ofoperation. The transmission unit 3 comprises a variator 9 and atransmission group10 shown in greater detail in FIG. 2, which comprisesrange clutches K1 to K3.

FIG. 2 shows a hydraulic circuit diagram of the hydraulic device 4 and agearwheel layout comprising the reversing gear system 6, thetransmission unit 3 and the drive output 5. The transmission unit 3 isconfigured with secondary coupled power branching and, by virtue of therange clutches K1 to K3, in the forward and reverse driving modesnon-synchronous range changes between three transmission ratio ranges ofthe transmission unit 3 can be carried out. Thus, the transmission unit3 is made with three driving ranges for forward and reverse driving,which can be obtained respectively by disconnecting one of the shiftelements K1, K2 or K3 and by connecting at least one of the shiftelements K1, K2 or K3.

Part of the torque provided in each case by the drive machine 7 can betransmitted in a first power branch 11 of the transmission unit 3 via ahydrostatic device 12 and the other part of the torque in a second powerbranch 13 via a mechanical device 14 between a transmission input 15 ortransmission input shaft and a transmission output 16 or transmissionoutput shaft. The two power branches 11 and 13 of the transmission unit3 are in active connection via a planetary gear system 17 of thetransmission unit 3.

Between a motor output shaft 18 of the drive machine 7 and thetransmission input shaft 15 is arranged a so-termed oscillation damper19, by means of which rotational irregularities in the area of the drivemachine 7 are damped so that only a small fraction of them gets throughto the reversing gear system 6 and the remainder of the vehicledrivetrain 1 of a vehicle or a construction machine.

The hydrostatic device 12 of the first power branch 11 comprises a pump20 and a motor 21 actively connected thereto by a hydraulic circuit (notshown in detail in the drawing), which are moved by a common yoke 22 andare designed as oblique axle units. However, depending on theapplication concerned, it is also possible for the pump and motor of thehydrostatic device to be adjusted independently of one another and tohave some other, also suitable structural form.

In addition, the transmission unit 3 and the reversing gear system 6 aremade as countershaft transmissions with a plurality of countershafts 23to 26 and 31, a distance apart from one another, such that thetransmission unit 3 and reversing gear system 6 take up relativelylittle structural space in the axial direction and a relatively largeamount of space in the radial or vehicle height direction, the largeradial space requirement being used to bridge an axial distance betweenthe motor output shaft 18 of the drive machine 7 or the transmissionoutput shaft 16 and the driven axles of the vehicle in this case made asa wheel loader.

In the present case the reversing gear system 6 comprises two drivingdirection shift elements KR and KV, by means of which the mode can beswitched between forward driving and reverse driving. On thecountershaft 26 associated with the drive direction shift element KR forreverse driving is arranged a geared pump 27, so that the countershaft26 can be driven by the drive machine 7 via a gearwheel pair 28.

The transmission ratio of the gearwheel pair 28, which is formed of afirst gearwheel 29 connected in a rotationally fixed manner on the othercountershaft 31 of the reversing gear system 6 and is made as a spurgear, and a second gearwheel 30, is such that the rotation speed of theother countershaft 31 in the direction of the countershaft 26 of thereversing gear system 6 is stepped up. Consequently, the geared pump 27in this case runs at a speed 20% higher than the drive machine and, withthis design of the reversing gear system 6, can be made smaller comparedwith a geared pump arranged directly on the countershaft 31 whichrotates substantially at the same speed as the drive machine 7.

By means of the geared pump 27, besides a hydraulic circuit thatconnects the pump 20 and the motor 21 of the hydrostatic device 1 to oneanother, this being formed as a closed circuit, a lubrication andcooling circuit as well can be pressurized with hydraulic fluid. Inaddition the shift elements K1 to K3 and the drive direction shiftelements KR and KV can be pressurized by the geared pump 27 to theirhydraulic working pressure and thus changed from an essentiallydisengaged, to an essentially fully engaged operating condition.

Besides the geared pump 27, in the area of the countershaft 26 of thereversing gear system 6 a further power take-off takes place, which isprovided for actuating the working equipment of a construction vehiclepreferably made as a wheel loader. In this context hydraulic cylindersarranged in an open hydraulic circuit, by means of which a loading scoopor suchlike can be actuated, are supplied with a corresponding workingpressure.

Both the shift elements K1 to K3 and also the drive direction shiftelements KR and KV are in the form of frictional shift elements, so thatnon-synchronous range changes between the driving ranges that can beengaged and disengaged by means of the three shift elements K1 to K3 canbe carried out.

The planetary transmission device 17 in this case comprises two sungears 32, 33 which mesh with common double-planetary wheels 34 which, inturn, are mounted to rotate on a planetary gear carrier 35. The othercountershaft 31 of the reversing gear unit 6 can be brought by means ofthe drive direction shift elements KV and KR into active connection withthe planetary carrier 35 of the planetary transmission device 17, whilethe pump 20 of the hydrostatic device 12 is connected to the small sungear 33 of the planetary transmission device 17. The large sun gear 32of the planetary transmission device 17 is connected in a rotationallyfixed manner to a gearwheel 37 through a ring gear 36 of the planetarytransmission device 17 made as a hollow shaft.

As a function of displacement of the motor 21 and a delivery volume ofthe pump 20, at least part of the torque applied by the drive machine 7can be transmitted, via the large sun gear 32 of the planetarytransmission unit 17, to the second power branch 13 containing themechanical device 14.

Basically, in the example embodiment of the vehicle drivetrain 1represented in FIG. 2 the drive input of the drive machine 7 is passedby the drive direction clutch KR or KV to the planetary carrier 35 ofthe planetary transmission unit 17. Starting from the planetary carrier35, the torque is divided by the double-planetary gears 34 and part ofit is passed on via the small sun gear 33 and used for driving the pump20. The mechanical drive output of the other part of the drive outputtorque of the drive machine 7 passes via the large sun gear 32 of theplanetary transmission unit 17 and the gearwheel 37 or the ring gear 36and a gearwheel 38 in turn connected in a rotationally fixed mannerthereto.

If the motor 21 is static and the pump 20 is rotating at its maximumspeed, the displacement of the motor 21 is a maximum whereas thedelivery volume of the pump 20 is zero. Thus, no drive power istransmitted to the drive output. It is then possible to support torqueacting from the vehicle completely hydraulically. If now, starting fromthis position of the hydrostats, the delivery volume of the pump 20 isincreased and if necessary the displacement of the motor 21 is reducedat the same time, then on the one hand the pump 20 begins delivering oiland taking up torque, and on the other hand the motor 21 begins turningand supplying a torque.

To maintain torque equilibrium at the planetary transmission 17, fromthe moment when the pump 20 takes up torque it is braked. Thus, fromwhen movement begins some power flows mechanically.

The second limit of the driving ranges that can be obtained with theshift elements K1 to K3 exists when the pump 20 is static and the speedof the motor 21 is at a maximum, the displacement of the motor 21 thenbeing zero and the delivery volume of the pump 20 at its maximum. Inthis operating condition of the hydrostatic device 12, the drive powerof the drive machine 7 is transmitted via the transmission unit 3completely mechanically by the other countershaft 31 of the reversinggear system 6 to the transmission output shaft 16 of the transmissionunit 3.

The largest transmission ratio can be obtained in the first drivingrange that can be engaged by means of the first shift element K1,whereas medium transmission ratios can be obtained in the second drivingrange that can be engaged using the second shift element K2 and thelowest transmission ratio in the third driving range that can be engagedusing the third shift element K3. Furthermore, the three driving rangesare designed in such manner that the first driving or transmission ratiorange and the second transmission ratio range and the third transmissionratio range overlap so that the transmission ratio in the transmissionunit 3 can be changed over the full transmission ratio range of thetransmission unit 3, which extends from the lower transmission ratiolimit of the first driving range up to the upper transmission ratiolimit of the third driving range, in a continuous manner, free fromtraction force interruptions and hardly perceptible by a driver of avehicle built with the transmission unit 3.

In the first driving range engaged using the first range clutch K1,depending on the operating condition of the hydrostatic device 12 thedrive torque of the drive machine 7 is transmitted at least in part bythe motor 21 via a spur gear 39 connected in a rotationally fixed mannerthereto and a further spur gear 40 that meshes with the latter. The saidfurther spur gear 40 is mounted to rotate on the countershaft 24 and canbe connected by means of the first shift element K1 rotationally fixedto a gearwheel 41, which is also made as a spur gear and is connected ina rotationally fixed manner on the countershaft 24. This means that witha corresponding transmission capacity of the first shift element K1 madeas a friction clutch, the hydraulically transmitted part of the torqueof the drive machine passes to the spur gear 41. In turn, the spur gear41 meshes with another gearwheel 42 connected in a rotationally fixedmanner to the transmission output shaft 16, by which the torque can betransmitted to the driveshaft of the vehicle.

The other part of the drive torque of the drive machine 7, when thefirst driving range is engaged, is passed by the large sun gear 32 andthe gearwheel 38 connected in a rotationally fixed manner thereto and bya further gearwheel 43 that meshes with it, to the countershaft 23 whichis connected in a rotationally fixed manner to the motor 21 and the spurgear 39. Thus, the part of the drive torque of the drive machine 7passed on by the mechanical device 14 is superposed on the part of thedrive torque transmitted by the hydrostatic device 12 already in thearea of the countershaft 23, and then passed on conjointly, via the spurgears 39, 40, 41 and 42, to the transmission output shaft 16.

When the second driving range is engaged, then a fraction of the drivetorque of the drive machine 7 that depends on the operating condition ofthe hydrostatic device 12 is passed by the motor 21, via thecountershaft 23 and the gearwheel 43 connected in a rotationally fixedmanner thereto, to the gearwheel 38 connected in a rotationally fixedmanner to the ring gear 36 of the planetary transmission unit 17. In theplanetary transmission unit 17, the torque applied to the ring gear 36is superposed on the part of the drive torque of the drive machine 7applied to the large sun gear 32 and then transmitted, via the gearwheel37, to a further gearwheel 44 mounted to rotate on the countershaft 25,and which meshes with the gearwheel 37. Since when the second rangeclutch K2 is engaged the gearwheel 44 is connected in a rotationallyfixed manner to the countershaft 25, the torque applied to the gearwheel44 is passed on to a gearwheel 45 connected in a rotationally fixedmanner to the countershaft 25, which in turn meshes with the gearwheel41 of the countershaft 24 so that the torque is transmitted from thespur gear 41 to the gearwheel 42 and therefore to the transmissionoutput shaft 16.

If the third driving range is engaged in the transmission unit 3, then afraction of the drive torque of the drive machine 7 that depends on thecurrent operating condition of the hydrostatic device 12 is passed onvia the first power branch 11, hydraulically by the motor 21 via thethird range clutch K3 and via a gearwheel 46 that can be connected in arotationally fixed manner by the third shift element K3 to thecountershaft 23, a gearwheel 47 which meshes with it, which is connectedto the countershaft 24, and the spur gear 41 also connected in arotationally fixed manner to the countershaft 24, to the gearwheel 42and the transmission output shaft 16. At the same time the other part ofthe drive torque of the drive machine 7 is passed along the second powerbranch 13 of the transmission unit 3, via the double-planetary gears 34and the ring gear 36 of the planetary transmission unit 17, to thecountershaft 23 and is there superposed on the torque delivered by themotor 21 and passed on, via the gearwheel chain already described, tothe transmission output shaft 16.

To engage one of the three driving ranges, in each case one of the shiftelements K1 to K3 must be adjusted to a transmission capacity at which atorque to be passed on from the transmission unit 3 can be transmittedin full by one of the shift elements K1 to K3. This means that when thefirst driving range is engaged, the first shift element K1 ispressurized with a working pressure at which the first shift element K1is completely engaged. In this operating condition of the transmissionunit 3 the other two shift elements K2 and K3 are essentiallydepressurized and are therefore in the disengaged condition.

When changing from the first to the second driving range, starting fromthe first shift element K1 a load transfer toward the second shiftelement K2 takes place, so that the first shift element K1 is the one tobe disengaged and the second shift element K2 is the one to be engaged.When a change from the second to the third driving range is required,the second shift element K2 is disengaged and the third shift element K3is engaged.

If now a change, respectively from the third to the second driving rangeor from the second to the first driving range is required, thenrespectively the third shift element K3 or the second shift element K2is the one to be disengaged while the second shift element K2 or thefirst shift element K1 is the one to be engaged.

Since in the area of the mechanical device 14 a change of the drivingrange also changes the transmission ratio fixed in each case by thevarious gearwheels of the mechanical device 14, in the area of thehydrostatic device 12 a change of the transmission ratio is carried outin the area of the hydrostatic device 12 by adjusting the displacementof the motor 21 and the delivery volume of the pump 20, with the resultthat at the end of the driving range change the transmission ratio inthe transmission unit 3 as a whole is the same as it was before thedriving range change and the overall transmission ratio of thetransmission unit 3 can be varied continuously over the full operatingrange of the transmission unit 3.

By virtue of the hydraulic device 4 arranged in the power flow betweenthe reversing gear system 6 and the drive machine 7, a vehicle made withthe vehicle drivetrain 1 can be operated purely hydraulically or purelyhydrostatically, so that the drive machine 7 then provides essentiallyno drive torque at the drive output 5 and is decoupled from theremainder of the vehicle drivetrain in the area of a shift element 60 orseparating clutch arranged between the drive machine 7 and the reversingunit 6, so as not to introduce any drag torques that would compromisethe hydraulic drive into the vehicle drivetrain 1. In addition, when theshift element 60 is engaged hybrid driving operation can be obtained bymeans of the hydraulic device 4 and the drive machine 7, during whichtorque is introduced into the power flow of the vehicle drivetrain 1both by the hydraulic device 4 and by the drive machine 7.

Such hybrid driving operation can take place both in traction operationand in thrust operation of the vehicle drivetrain 1. During thrustoperation of the vehicle drivetrain 1, in the area of the hydraulicdevice 4 at least part of the drive torque to be supported can be usedfor recovering energy by recuperative operation of the hydraulic device4 in the manner described later.

The hydraulic device 4 comprises a hydraulic machine 47 that can beoperated in both rotational directions, which is connected via a spurgear pair 48 to the transmission input 15 in the area of the planetarycarrier 35 of the planetary transmission unit 17. The hydraulic machine47 is also built to swivel in both directions and the suction side andpressure side of the hydraulic machine 47 are identical over the entireoperating range of the hydraulic machine 47. The spur gear pair 48comprises a spur gear 50 connected in a rotationally fixed manner to anoutput shaft 49 of the hydraulic machine 47, which meshes with thegearwheel 29 of the reversing gear system 6.

The output shaft 49 of the hydraulic machine 47 is connected in arotationally fixed manner to an auxiliary drive output shaft 52 by meansof which further auxiliary outputs of the vehicle made with the vehicledrivetrain 1 can be driven.

The hydraulic machine 47 is actively connected on its suction side witha substantially unpressurized hydraulic fluid reservoir 54 and on itspressure side to a pressure medium container unit 55, which in thepresent case comprises three containers. The number of containers of thepressure medium container unit varies depending on the application ineach case and on the extent of energy storage required. In the exampleembodiment of the device 2 represented in the drawing, the hydraulicfluid reservoir 54 is also the fluid reservoir of the vehicle's workingmachine. In other embodiments of the device the hydraulic fluidreservoir of the device is made separately from the fluid reservoir ofthe working machine, which emphasizes the modular nature of the deviceaccording to the invention.

Between the pressure side of the hydraulic machine 47 and the pressuremedium container unit 55 is arranged a one-way valve device 56 that canbe actuated, which blocks the connection between the hydraulic machine47 and the pressure medium container unit 55, if there exists a positivepressure gradient between the pressure container device 55 and thepressure side of the hydraulic machine 47. This one-way valve device 56can be actuated by means of 3/2-way valve 59, whereby the responsebehavior of the one-way valve device 56 can be varied as a function ofpressure.

To enable a maximum operating pressure of the hydraulic device 4 to belimited, the hydraulic device 4 comprises a pressure-limiting valvedevice 57. In addition, a storage pressure of the pressure mediumcontainer unit 55 is determined by a pressure sensor 58. The pressuresignal from the pressure sensor 58 is used for the operation strategy ofthe hybrid drive of the vehicle drivetrain 1. For example, if a storagepressure close to the gas filling pressure is determined, thedisplacement of the hydraulic machine 47 is reduced to zero.

If a positive torque or drive is to be introduced into the force flow ofthe vehicle drivetrain 1 by the hydraulic machine 47, the connectionbetween the pressure medium container unit 55 and the hydraulic machine47 is opened in the area of the unblocking one-way valve 56 byappropriately switching the 3/2-way valve. The pressure medium stored inthe pressure medium container unit 55 then drives the hydraulic machine47, in the area of which the hydraulic pressure is converted tomechanical energy. During this driving mode of the hydraulic machine 47the pressure medium used from the pressure medium container unit 55 isdelivered to the hydraulic machine 47 via its pressure side and then,via the suction side of the hydraulic machine 47, returned to thehydraulic fluid reservoir 54.

During a recuperative operation of the hydraulic device 4 part of thedrive torque to be supported is passed into the hydraulic machine 47 bythe spur gear pair 48. The hydraulic machine 47 draws hydraulic fluidout of the hydraulic fluid reservoir 54 and pumps it through the one-wayvalve device 56, which opens above a pre-set pressure level, into thepressure medium container unit 55. If a maximum operating pressure isreached in the area of the pressure-limiting valve device 57, thepressure-limiting valve device 57 opens a connection, upstream from thepressure medium container unit 55, between the pressure side of thehydraulic machine 47 and the hydraulic fluid reservoir 54, wherebyexcess hydraulic fluid flows back into the hydraulic fluid reservoir 54through a cooler (not shown).

The advantage of the hydraulic shifting of the hydraulic device 4 isthat the hydraulic fluid volume flow that passes in each case betweenthe pressure medium container unit 55 and the hydraulic machine 47 inorder to operate the latter does not pass through the 3/2-way valve butonly through the one-way valve device that can be unblocked, so thathydraulic losses are low.

Basically, the hydraulic device 4 can be produced simply andinexpensively since it is made using conventional structural components.By virtue of the hybrid drive that can be obtained with the hydraulicdevice 4 and the drive machine 7, which can be in the form of a dieselinternal combustion engine, the latter can be made smaller by comparisonwith conventional vehicle drivetrains. Moreover, by means of thehydraulic device 4 so-termed boost operation is possible, and theoperating point of the drive machine 7 can also be displaced during acharging operation of the pressure medium container unit 55 on the partof the device.

INDEXES

-   1 Vehicle drivetrain-   2 Device-   3 Transmission unit-   4 Hydraulic device-   5 Drive output-   6 Reversing gear system-   7 Drive machine-   8 Auxiliary drive output-   9 Variator-   10 Transmission group-   11 First power path-   12 Hydrostat device-   13 Second power path-   14 Mechanical device-   15 Transmission input-   16 Transmission output-   17 Planetary gear system-   18 Motor output shaft-   19 Oscillation damper-   20 Pump-   21 Motor-   22 Yoke-   23-26 Countershaft-   27 Transmission pump-   28 Gearwheel pair-   29, 30 Gearwheel-   31 Further countershaft of the reversing gear system-   32 Large sun gear-   33 Small sun gear-   34 Double planetary gear-   35 Planetary carrier-   36 Ring gear-   37, 38 Gearwheel-   39-41 Spur gear-   42-46 Gearwheel-   47 Hydraulic machine-   48 Spur gear pair-   49 Output shaft-   50, 51 Spur gear-   52 Auxiliary drive output shaft-   54 Hydraulic fluid reservoir-   55 Pressure medium container unit-   56 One-way valve device-   57 Pressure-limiting valve device-   58 Pressure sensor-   59 3/2-way valve-   60 Shift element, separating clutch-   K1 to K3 Range clutch-   KV, KR Driving direction shift element

1-11. (canceled)
 12. A device (2) for a vehicle drivetrain (1) with atransmission unit (3) for changing various transmission ratios, with ahydraulic device (4) by which a drive torque is provided in an area of adrive output (5) of the vehicle drivetrain (1) and in whose area a driveoutput torque of the vehicle drivetrain (1) is at least partiallysupported upstream of the transmission unit (3), a reversing gear system(6) being connected for reversing a rotation direction, and thehydraulic device (4) being actively connectable with the transmissionunit (3) by the reversing gear system (6).
 13. The device according toclaim 12, wherein a plurality of range clutches (K1, K2, K3) areprovided in an area of output (16) of the transmission unit (3) forobtaining various transmission ratio ranges, and within the area ofoutput (16), the transmission ratio of the transmission unit (3) isvaried continuously in each case.
 14. The device according to claim 12,wherein the hydraulic device (4) is actively connectable, via a firstgearwheel (50), with a gearwheel (29) of the reversing gear system (6).15. The device according to claim 12, wherein the hydraulic device (4)is connected to an auxiliary drive output shaft (52).
 16. The deviceaccording to claim 12, wherein the hydraulic device (4) comprises ahydraulic machine (47) which is operable in both rotation directions.17. The device according to claim 16, wherein the hydraulic machine (47)has a pressure side that is actively connected to a pressure mediumcontainer unit (55) and a suction side that is actively connected to ahydraulic fluid reservoir (54).
 18. The device according to claim 17,wherein a one-way valve (56) is arranged between the pressure side ofthe hydraulic machine (47) and the pressure medium container unit (55),and the one-way valve (56) is actuated to block the connection betweenthe hydraulic machine (47) and the pressure medium container unit (55)if a positive pressure gradient exists between the pressure mediumcontainer unit (55) and the pressure side of the hydraulic machine (47).19. The device according to claim 18, wherein the one-way valve device(56) is actuated by a 3/2-way valve.
 20. The device according to claim12, wherein the hydraulic device (4) comprises a pressure-limiting valvedevice (57) for limiting a maximum operating pressure.
 21. The deviceaccording to claim 17, wherein a pressure sensor (58) monitors a storagepressure of the pressure medium container unit (55).
 22. The deviceaccording to claim 12, wherein a shift element is located between aconnection area of the hydraulic device (4) and the reversing gear unit(6), and an area of the vehicle drivetrain (1) in which a drive machine(7) of the vehicle drivetrain (1) is coupled to the reversing gear unit(6), the shift element optionally produces the active connection betweenthe drive machine (7) and the reversing gear unit (6) and the hydraulicdevice (4) that can be coupled thereto.